At least one embodiment of the invention relates to a standpipe arrangement and fastening for holding and for supplying gas to aerators in a waste water clarifying basin.
Normally aerators in a waste water clarifying basin are arranged on the edge of the basin, as the introduced gas rises upwards, and only through arranging the aerators on the edge of the basin is it ensured that all layers of the waste water are supplied with gas. As a rule, mechanical stirring mechanisms are also built into the basin, which bring about additional mixing of the waste water.
When arranging the aerators in the basin as flat a configuration as possible should be aimed for. This ensures that all areas in the basin are evenly supplied with air. Depending on the basin configuration an aeration system is efficient to a greater or lesser extent.
As the aerators have a defined and standard opening pressure, with a view to efficient and uniform aeration of the waste water it is also necessary to install the aerators at a uniform height level. Otherwise aerators in a higher position would aerate better than those in a lower position due to the low counter-pressure of the smaller water column, so that the uniform and planar aeration of the waste water would be disrupted, resulting in a loss of efficiency.
Fastening of the aerators on the base of the basin is necessary to stop the aerators floating upwards and so that their position is not changed through flows such as those produced by the stirring mechanisms and also by the introduced air. Usually the aerators are mounted on, and supplied with gas via distributor pipes made of stainless steel or plastic. The distributor structures are connected to each other by means of screw, adhesive or welded connections and fastened to the base of the basin with separate elements.
A pipe conduit of a conventional standpipe arrangement thus comprises several elements. By assembling these different elements with each other various pipeline lengths can be produced.
In order to fasten the aerators to the pipe conduit they are inserted into holes. Generally the aerators are attached perpendicularly to the pipes and are located either on the pipes or are attached laterally.
In order to be able to install all the aerators on one level, the pipe conduits are fixed to the base of the basin so that levelling both in the horizontal and vertical axis is possible. For this, in the case of stainless steel pipes, brackets are welded onto the pipe at defined intervals. These brackets are provided with a hole through which is passed a threaded anchor inserted in the base of the basin. By way of nuts provided above and below the brackets the pipe structure can be positioned at the required height.
When using plastic pipe conduits, a firm connection of the pipes to the base of the basin can only be achieved in a costly and laborious manner. This is because depending on the water depth, water temperature, air temperature and course of the pipes, more or less hot air is introduced via the pipe conduits into the aerators, as a result of which expansion or contraction of the pipes due to the thermal properties of the plastics takes place.
Fixing of the pipes to the base of the basin by means of brackets or similar measures which do not allow longitudinal expansion would not therefore be possible.
Nonetheless the pipe conduits must be secured against buoyancy and flow-induced movements, and levelling as described above must be permitted.
To attach the plastic pipe conduit to the base of the basin mechanically complex fastening clips are therefore usually provided. These surround the pipe conduit with a defined clamping force and thereby permit expansion of the pipes in the longitudinal direction. The pipe can move longitudinally within the clip as the clamping force is defined so that movement of the pipe conduit in the longitudinal direction is possible.
However, the use of these clips considerably restricts configuring the basin with aerators, as no aerators can be arranged in the clip areas and depending on the expected longitudinal expansion, a gap must be maintained between the fastening and aerator so that expansion of the pipe conduit is not hindered by the aerator mounted on or at the pipe conduits. A significant loss of efficiency is caused by these interruptions in the configuration.
To achieve the necessary height levelling, the fastening clips are designed so that they can be elevated by way of a foot structure. For this, a plate in which holes are made is normally attached to the lower end of the clip. By way of these holes, the structure is firmly connected to threaded anchors inserted in the base. Via the thread, levelling takes place with nuts which are then screwed against each other to fix the height of the pipes.
In the case of stainless steel pipes, several pipe conduits are usually connected to each other by welding. Where welding is not possible the pipe conduits are connected to each other via couplings by means of flanges or other screw and clamp connections. In both cases, the joining of two pipe conduits to one another constitutes at least one additional working step.
Particularly in the case of welding, additional refinishing work also has to be performed on the connection seam again as the welding seam must be separately pickled in order to prevent corrosion.
Although the refinishing work is omitted in the case of coupled connections, assembly is critical, as well as being laborious and risky in terms of correct attachment of the coupling, as incorrect positioning of a clip would result in leakages.
When using plastic pipes several pipe conduits are connected to each other by means of adhesion, welding or coupling.
In the case of welding, hot-tool welding is used, whereby the ends of the pipe conduits to be connected are softened through the use of heat so that on connecting the sections interfusion of the materials occurs.
However, the adhesion and welding of plastic material is technically complex and also only possible under certain general conditions. Both methods can only be used within a limited temperature range. Here, both the ambient temperature and the temperature of the material are of relevance. Particularly, in view of the fact that the adhesion and welding work is performed in the waste water basin, additional demands are made on the processing. For example, separate basin covers have to be provided so that no moisture reaches the point on which the work is to be carried out, or the basins have to be thoroughly cleaned before assembly.
When using plastic pipes, an adhesive or welded connection is also a weak point due to the low impact resistance and tensile strength of the plastic. Especially so as the aerators are applied perpendicularly to the pipe conduit and as a result of this the flow energy is increasingly introduced into the support pipes via the aerators. The occurring oscillation and bending forces can be so great that the pipe conduit is torn open or the adhesive or weld connection between the pipe conduits is destroyed.
In addition to the restricted temperature range, adhesive and welded connections have the drawback that further processing is only possible after a certain hardening time. If the further processing, for instance in the form of mounting the aerators, occurs before the connection points have completely hardened, the setting process is disrupted by the movement of the aerator and the parts cannot be durably and securely connected.
Through this technical condition assembly is on the one hand retarded and interrupted, and on the other hand the risk of assembly errors due to not observing the hardening specifications is considerably increased.
Over and beyond this feature, an adhesive connection has the disadvantage that the adhesive is exposed to water and can be degraded. Furthermore, the high air temperatures cause the adhesive to soften so that the connection is loosened.
In addition, there are plastic materials which cannot be durably adhered to one another and/or adhesives have to be used which both damage the environment and are harmful to health.
To prevent damage to the pipe conduit caused by vibrations and other forces introduced into the pipeline via the aerators, large wall thicknesses as well as more solid type of connection are used. However, using more solid materials simultaneously influences the expansion of the pipe conduits. This is because a thick-walled pipe expands more so that additional measures have to be taken. Moreover, the use of more solid pipes is expensive and makes processing more difficult.
Coupling of the plastic pipes is certainly technically possible, but poses a problem against the background of thermal expansion. The couplings are not always obtainable in exactly the same material that the pipes are made of. As a result, due to the different expansion coefficients of the material, differences in expansion occur so that leaks can occur in the region of the connection point.
In addition to the problems relating to the connection of plastic pipe conduits, with every type of connection the provision of the basin with aerator elements is interrupted, as in the area of the connection no drilled holes to hold the aerators can be produced so that when using plastic pipe conduits there is an interruption in at least two points per pipe conduit, resulting in a considerable loss of efficiency and performance.
Another problem is securing the pipe conduits against rotary movements initiated by the aerators. The fastening clips applied to secure the pipe conduits against buoyancy on the base of the basin and which only surround the pipe conduits but are not firmly connected to them, cannot absorb torsion forces. As a consequence, all the kinetic energy introduced into the pipe by way of the aerators is taken up by the connection elements. Due to the relatively low strength of plastic materials and against the background that the connections are only adhesive or welded connections in places, the fact that the connection elements have to absorb the high torsion force constitutes a considerable operational risk. In many applications damage to the pipeline system occurs because of this problem.
In addition, the force introduced by the up and down movements of the ends of the aerators can lead to destruction of the connection point between the aerator and the pipe conduit, whereby the aerators really tear open the pipe conduits. This is because due to the acting forces the already relatively weak plastic material is further weakened by the holes produced in the area in which the aerators are applied.
The application of the aerators on the pipe conduits also leads to a general weakening of the material. The pressure acting on the support pipes through fastening the aerators thereon causes the plastic material to flow; it effectively evades the pressure whereby not only is the wall thickness in the area of the fastening reduced, but flowing of the material brings about a change in the external diameter of the pipe which results in a reduction in the clamping force which is necessary for the aerator to be firmly attached on or to the pipe conduit. This leads to leakages or even loosening of the aerators.
In addition to this, the no longer firm attachment of the aerators to or on the pipe conduit can lead to increased vibration of the aerators as a result of which the support pipe is weakened further in the area of the fastening.